Quantitative receptor autoradiography with tritium-labeled ligands: comparison of biochemical and densitometric measurements.

Tritium-labeled receptor ligands are commonly used for quantitative receptor autoradiography with LKB Ultrofilm. In this study, we compared estimates of tritium concentrations by optical density measurements with direct measurements of tritium concentrations by scintillation counting. We found that predominantly grey matter regions of rat brain showed similar tritium concentrations when measured by either method, but that optical density reading of white matter regions indicated a lower tritium concentration than determined by direct measurement with scintillation counting. We also compared measurements of receptor density by quantitative autoradiography with radioligand-binding measurements on microdissected brain regions. Higher per milligram protein levels of muscarinic receptors were obtained by quantitative autoradiography, comparable to the specific activity of receptors found in purified membranes.